This invention relates to operation of electron discharge devices, such as fluorescent lamps, that require the use of a ballast circuit for plasma induced current starting purposes.
Generally, the ballast circuit with multiple fluorescent lamps includes a power supply transformer having a plurality of low voltage windings connected to the opposite filaments of the lamps, with a starting capacitor connected across one pair of filaments of one of the lamps. Various regulated devices for ballasted fluorescent lamps are known or have been proposed to assist starting, protect lamp filaments and other related purposes. For example, each of U.S. Pat. Nos. 4,101,806 and 4,410,836 to Alley and Roche, respectively, show two fluorescent lamps having filaments interconnected externally of the lamps and coupled to one of the secondary winding of a ballast transformer with the other filaments of the respective lamps being coupled to two other secondary windings of the transformer. The latter patents also show a starting capacitor connected across the filaments within one of the lamps as part of a ballast starting control system.
Other ballast regulating techniques are known, such as the use of diodes coupling the secondary winding of the ballast transformer to both filaments of a single lamp, such diodes interacting with each other for the purpose of switching the supply of current to only that one of the filaments having the higher potential in order to maintain a constant temperature despite wide current variations from the power source. Such diode arrangement is disclosed in German Pat. No. 2,755,614. U.S. Pat. No. 4,227,118 to Britton also shows a single lamp to which current is supplied through a ballast capacitor and an inductor acting as a voltage doubler and interacting with a Zener diode and thyrsistor coupled to the other filament of the lamp to achieve more rapid ignition of the lamp. Neither of the latter patents relates to ballast control peculiar to series connected lamps which interact in response to current control exercised with respect to one of the lamps.
It is therefore, an important object of the present invention to provide a control attachment to the ballast arrangement associated with two interconnected fluorescent lamps for modifying joint ignition of such lamps under existing ballast control to reduce energy consumption both during the start-up operation and the steady state running operation without adversely affecting restart.
It is an additional object of the present invention to provide a low cost current control device capable of being readily interfaced with existing ballast circuits for two or more fluorescent lamps to improve ballast efficiency, reduce current consumption and prolong lamp life expectancy.